In recent years, active development is performed on a head-mounted type image display device that can be attached to eyeglasses or the like, aiming at practical applications such as video viewing and information display for use in a mobile terminal. The device is generally referred to as “head-mounted display (HMD)”, in which an image light beam from a display element is guided to an eye pupil so as to be imaged onto a retina, to thereby allow the wearer to observe the image as an enlarged virtual image.
FIG. 13 is a schematic view illustrating a configuration of a general head-mounted image display device 1310. In FIG. 13, an image light beam 1312 of an image X displayed by a display element 1311 is incident on a light-guide portion 1313 and reflected therewithin at least once before being emitted from the light-guide portion 1313. The image light beam emitted from the light-guide portion 1313 enters an eye pupil of an eyeball 1320 of a wearer to form an image onto a retina, to thereby allow the wearer to observe a virtual image X′ of the image X ahead in the direction of the visual axis of the eye pupil.
The eye pupil herein refers to a portion 1402 bounded by an iris 1401 of the eyeball 1320 as illustrated in FIG. 14, and light that has passed through the portion 1402 is projected onto a retina 1403. Accordingly, in order to properly observe the whole display image, the exit pupil of the light-guide portion and the eye pupil 1402 need to be in line with each other.
However, there are individual differences in position of an eyeball and of the eye pupil of the wearer, and thus the exit pupil of the light-guide portion and the eye pupil may be misaligned, which leads to problems in that part of the image light beam does not enter the eye pupil to cause eclipse, or in that all the image light beams do not enter the eye pupil and nothing can be observed. In particular, a small-scale optical system has a relatively small exit pupil, and is more susceptible to the misalignment ascribable to the interpupillary distance of the wearer or the frame shape of the eyeglasses on which the device is to be mounted.
Patent Literature 1 (PTL 1) discloses a display device including: a combiner optical system incorporated in an eye glass lens; a display panel; and a condenser lens disposed between the display panel and the combiner optical system, in which the display panel and the condenser lens are moved together relative to the combiner optical system, or the combiner optical system, the display panel, and the condenser lens are integrally moved all together, to thereby adjust an eye point position serving as an exit pupil of the combiner optical system.